For the purpose of more adequately describing a technological level for the present invention at present, all descriptions of the patents, patent applications, patent gazettes, scientific papers, and the like which are cited or specified in the present application will be incorporated herein by reference.
Conventionally, an LSI test socket (hereinafter, referred to as an LSI socket) has been used to avoid thermal and mechanical damage to a solder ball in a BGA package when conducting a screening test on LSI incorporated in a high-density and multi-pin BGA package. An LSI socket used to accomplish this objective is largely divided into two types: a pogo-pin type and a sheet type.
The pogo-pin is called a spring pin or a spring probe pin, and composed of three components: a pogo-pin 001, a pin 002, and a spring 003, as shown in the cross-sectional view of FIG. 1. A pogo-pin type LSI socket using this pogo-pin is provided together with a pin in which coiled spring structure is supported by a resin casing to press above and below this pin, thereby providing the realization of an electrical connection.
FIG. 2A, FIG. 2B, FIG. 3A, and FIG. 3B are cross-sectional views showing the structure of conventional LSI sockets for BGA using pogo-pins, respectively. First, as shown in FIG. 2A and FIG. 2B, this LSI socket is composed of the pogo-pin 001 and a pogo-pin supporting casing portion 005 in combination. More specifically, the LSI socket has structure in which the pogo-pin 001 is inserted into a casing hole 010 from the upper side or the lower side of the pogo-pin supporting casing portion 005 which is made of nonconductive material such as resin.
FIG. 2A is a case in which the pogo-pin 001 is inserted into the casing hole 10 from the downside of the pogo-pin supporting casing portion 005 and fixed, with stoppers 006 located on the upper side of the pogo-pin supporting casing portion 005. On the other hand, FIG. 2B is a case in which the pogo-pin 001 is inserted into the casing hole 010 from the upper side of the pogo-pin supporting casing portion 005 and fixed, with the stoppers 006 located on the downside of the pogo-pin supporting casing portion 005.
In addition, FIG. 3A is a case in which the LSI socket with the structure of FIG. 2A is disposed on a test board 009, and FIG. 7B is a case in which the LSI socket with the structure of FIG. 2B is disposed on the test board 009. In either case, the pogo-pin 001 which is located corresponding to the position of a solder ball 007 of the LSI enclosed in the BGA package provides the realization of the electrical connection by pressing a wiring pad 008 on the test board 009 on which the LSI socket is mounted from above. In general, it is an advantage that this type of LSI socket is cheap in price because of simple structure, and may be repeatedly used because of great mechanical strength.
On the other hand, a sheet type LSI socket involves the use of a conductive sheet, and includes a metal fine wire embedded type and a conductive rubber type. The sheet type one may be shortened more than the aforementioned pogo-pin type one in pin length, and has the advantage of excellence in high frequency characteristics. However, the sheet type one has problems with much dust caused by metal oxide shavings, and high running cost due to expensive sheet, and further a problem with larger contact resistance because metal oxide is attached to the contacting surface.
Additionally, in the case of using any of these types of LSI sockets, a significantly serious problem has emerged along with high frequency and high power current operation of LSI in recent years. Test frequencies have become higher along with considerable performance improvement of LSI to be tested, and test conditions of the LSI incorporated in the BGA package have been conducted in a high frequency area of GHz order. This produces an extremely high power current, with the result that it is more likely that the potential fluctuation of power supplies and GNDs of the LSI occurs. There is another problem that it is difficult to supply power supplies with high quality in the vicinity of the BGA package because power supplies required for LSI operation are supplied from a tester far distant from the LSI when conducting an LSI screening test.
For this reason, if a capacitor cannot be disposed in the closest vicinity of a BGA package to be tested, a power current is produced by LSI high frequency operation to fluctuate the potential of power supplies and GNDs of the test board, leading to difficulty in ensuring operational stability of the LSI incorporated in the BGA package.
However, aside from this, a conventional LSI socket has an essential problem that a decoupling capacitor for reducing a swing of the potential fluctuation of the power supplies and the GNDs in the vicinity of the BGA package has become impossible to be mounted. It results from the facts that the number of electrodes of input/output signals, the power supplies and the GNDs of the LSI is increased by an improved integration degree more than before, and that the spacing between electrodes in the BGA package is narrowed to cause the electrodes to be densely packed by the miniaturization of the BGA package. In addition, even if the test frequency is less high, for example, LSI having as many as 512 of parallel input/output number has a problem that an enormously instantaneous power current flows at the time of 10 concurrent operation.
As a means of reducing the potential fluctuation of the power supplies and the GNDs described above, the sheet type LSI socket, for example, is intended to use a conductive sheet as a capacitor by connecting a plurality of electrodes on one side of the conductive sheet to a conductive layer, and allowing the conductive layer to be attached to the sheet to comprise a power supply layer, and by connecting a plurality of electrodes on the other side of the conductive sheet to the conductive layer, and allowing this conductive layer to be attached to the sheet to comprise a GND layer (for example, refer to Patent Document 1). This makes it possible to dispose a package sized capacitor immediately below the BGA package incorporating the LSI, whereby the effect of noise occurring in the power supplies and the GNDs at the time of the LSI high frequency operation may be reduced.
The conventional sheet type LSI socket described above has a problem with significantly difficulty in realization because of its structure, a problem with high running cost because of expensiveness and lack of sufficient stability for repeated use, and further a problem with lack of the contact ability of the LSI socket itself, with the result that it is not to be repeatedly used at a mass production level. Furthermore, the LSI in recent years mostly needs a plurality of power supply voltages, to which the sheet type cannot respond.
[Patent Document] Japanese Unexamined Patent Publication No. 2000-97991 (Page 3, FIG. 1 to FIG. 3)